Along with the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, importance has been attached to the development of batteries used as their power sources. Also in the automobile industry, development of high-power and high-capacity batteries for electric cars or hybrid cars is proceeding. Among various batteries, lithium batteries are now attracting attention for their high energy density.
Lithium batteries now commercially available use a liquid electrolyte containing a flammable organic solvent, and therefore it is necessary to install a safety device for suppressing temperature rise in the event of a short circuit or to improve their structure and materials to prevent a short circuit. On the other hand, it is considered that an all-solid-state lithium battery obtained by replacing a liquid electrolyte with a solid electrolyte layer is excellent in production cost and productivity, because a flammable organic solvent is not used in the battery and therefore a safety device can be simplified.
Such a solid state battery usually includes a cathode active material layer, an anode active material layer, and a solid electrolyte layer formed between the cathode active material layer and the anode active material layer. Further, the electrode active material layer (cathode active material layer and anode active material layer) is a layer which contains at least an active material, and may further contain a conductive material that improves electron conductivity and a solid electrolyte material that improves ion conductivity.
Patent Literature 1 discloses an electron-lithium ion mixed conductor using a transition metal sulfide represented by MeS (Me is a metal element mainly containing one or more transition metal elements), lithium sulfide, and silicon sulfide. According to this technique, a raw material (lithium sulfide, silicon sulfide, and the like) of a lithium ion conductor is doped with a transition metal sulfide to improve electron conductivity.